Final answer:
The pH of a 0.25 M solution of ammonium chloride is acidic and less than 7.00 because ammonium ionizes in water. Given the options provided, the correct pH value for the given concentration of ammonium chloride is (D) 4.50.
Step-by-step explanation:
The pH of a 0.25 M solution of ammonium chloride can be determined by considering the ionization of ammonium in water. Ammonium chloride (NH₄Cl) fully disassociates into ammonium ions (NH₄+) and chloride ions (Cl−). The ammonium ion is a weak acid and its ionization in water is represented by the following equilibrium reaction:
NH₄+(aq) + H₂O(l) ⇌ NH₃(aq) + H₃O+(aq)
The equilibrium constant (Ka) for the reaction of the ammonium ion is the inverse of the Kb of NH₃, which is 5.6 × 10−10. For a 0.25 M solution of NH₄Cl, the concentration of NH₄+ is initially 0.25 M. Using an ICE table, we can calculate the concentration of hydronium ions (H₃O+) produced and subsequently determine the pH of the solution. Since NH₄+ is the conjugate acid of a weak base (NH₃), the solution will be acidic, meaning that the pH will be less than 7.00. The only option less than 7.00 is (D) 4.50, which is the answer to this question.